Abd al-Malik bin Umayr said: I was present with Ali (may Allah be pleased with him) when al-Mustawrid bin Qabisah, a man of Banu Ijl, was brought, who had become a Christian after accepting Islam. Ali (may Allah be pleased with him) asked: What is this I have heard about you? He said: What have you heard? He said: I have heard that you have become a Christian. He said: I am on the religion of the Messiah. Ali (may Allah be pleased with him) said: I too am on the religion of the Messiah. Then Ali (may Allah be pleased with him) said: What do you say about him? He said something that was hidden from me, so Ali (may Allah be pleased with him) said: Trample him. So he was trampled until he died. I said to the one next to me: What did he say? He said: He said that the Messiah is his Lord.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16885